Manufacture of closure seals having formed cushion pads therein



Feb. 18, 1958 J, L. SCHNEIDER 2,823,422

MANUFACTURE OF CLOSURE SEALS HAVING FORMED CUSHION PADS THEREIN FiledNov. 1950 INVENTOR ATTORNEYS United States atent MANUFACTURE OF CLOSURESEALS HAVING FORMED CUSHION PADS THEREIN Julius L. Schneider, Chicago,Ill., assignor to Continental Can Company, Inc., New York, N. Y., acorporation of New York Application November 8, 1950, Serial No. 194,662

6 Claims. (Cl. 18-59) This invention relates to the manufacture ofclosure seals having formed cushion pads therein.

It has previously been proposed to make closure seals by employing aplastic material which is shaped by the action of a punch and therebycaused to conform to the shape of the crown shell, providing the pad inthe form of a structure having a thin central portion and a thickerannular portion for engaging with the lip of the container to be sealedby the closure seal. In practice, some difliculties have arisen withvariations 'of the plasticity of the material, wherewith imperfectionsoccurred at the annular portion, and flash was developed at theperiphery, extending into the region of the corrugated skirt parts ofthe crown shell. Such flash was particularly undesirable when the flowof the material was not regular, as for example when the mass developeda complete fill of the molding parts at one point of the periphery whileanother part of the periphery was unfilled: as in such cases theprotrusion of flash is local and eflicient use of the volume of materialis not attained. Two serious difficulties due to such flashing are theappearance of the finished closure, and the possibility that the flashedmaterial may loosen or be detached and thereby interfere with thesealing.

A feature of the present invention is to prevent the formation of suchflash, by confining the plastic material during its flow, so that acushion pad of the intended form is produced, and the extrusion of flashis eliminated.

Another feature of the invention is the use of a platen and punch setfor shaping such cushion pads, in which the platen supports the crownshell and employs the same as a female mold for the shaping of thecushion pad, while the punch is effective to displace the plasticmaterial, to confine it, and to cooperate with the shell in securing acushion pad of the intended shape. In a preferred form of practice forthis feature, the supporting surface of the platen, which acts as ananvil, has a lesser curvature, for example being flat, than the usualinternally radiused or dome-like surface of the bottom of the crownAnother feature of the invention is a method of shaping a cushion pad ina crown shell, by engaging the periphery of a punch surface with aninner surface of the crown shell and thereafter exerting pressure uponthe pad material to distribute it into the desired shape and therewithconfining the material for preventing theformation of flash and forassuring the production of a cushion pad surface competent of sealingagainst the container lip, and also assuring adhesion of the pad to thecrown shell adjacent the outer edge of the pad.

A further feature of the invention is the manufacture of a crown sealcomprising a crown shell and a cushion pad, this cushion pad having athin central portion and a thicker annular portion for engaging the lipof the container to be sealed, the annular portion being thicker at itsouter periphery than at its inner periphery.

A further feature of the invention is the manufacture of a crown sealcomprising a crown shell and a cushion pad therein, the cushion padhaving a thin central portion and a thicker annular portion, the annularportion having a bevel at its outer periphery leading from the exposedlipengaging surface of the annular portion to the top corner radius ofthe crown shell.

This essential elimination of flash permits the em-. ployment of lesserquantities with assurance of having a proper sealing surface andthickness on the cushion pad, as it is no longer necessary to makeallowance for flash. On the other hand, the confinement of the mass ofmaterial during the shaping operation establishes a greater tolerancewith respect to the quantity of material used in the blank, and thepositioning of this charge within the crown shell.

With these and other features as objects in view, an illustrativepractice of the invention is shown on the accompanying drawings inwhich:

Fig. 1 is a view showing a metal crown shell, partly in radial sectionand partly in elevation, to show a standard conformation thereof.

Fig. 2 shows such a crown shell present on a platen, and having a chargeof cushion pad material therein.

Fig. 3 shows the structures as in Fig. 2, with a punch exerting pressureupon the material being shaped to form the cushion pad.

Fig. 4 shows the structures of Fig. 3, with the punch having beenbrought down to its final relative position, and having accomplished theshaping of the plastic material into the cushion pad.

Fig. 5 shows the shaped crown seal comprised of crown shell and formedcushion pad, in diametrical section.

As shown in Fig. l, the crown shell employed in crown seals of currentpractice is made of sheet metal by blanking and forming operations sothat it has a concavely domed bottom portion 10 with a smoothly curvedperiphery leading to a corrugated skirt portion 11. This smoothly curvedperipheral portion 12 is known as the top corner radius. Asmanufactured, the crown shells of Fig. l have the corrugated skirtportion 11 extending angularly outward from the junction with the topcorner radius 12. In present practice, the crown shells as formed in thepunch press have a domed bottom with a radius in the range of six inchesto eight inches: this shape of bottom is referred to as top radius.

According to the present invention, such a crown shell is placed on aplaten 15, Fig. 2, which in the preferred form as illustrated, has aflat top surface for receiving the domed bottom 10 of the crown shell.It is preferred to have this platen heated to a temperature of flow ofthe plastic material as by a gas flame 16.

A standard quantity of the plastic material is measured and deposited asthe mass 17 in the crown shell S shown in Fig. 2. This material ispreferably of thermoplastic nature, so that it can be made more fluid byheating: and exhibits elasticity in its final cooled condition.

In Figure 3, a punch 20 has been brought down into contact with the mass17, and has begun to deform the same by causing parts of the mass toflow relatively radially outward from the position shown in Fig. 2. Inthe illustrated preferred form, the punch 20 has a projecting centralpart 21 having a fiat end surface. This punch has a conical shouldersurface 22 leading to the rebated part 23 of the end surface of thepunch 20 which is to produce the exposed surface of the thicker annularportion of the cushion pad: in the illustrated prefered form, thissurface 23 is also of conical shape. At the outer part of the endsurface of the punch 20, it is provided with a projecting rib 24, whichextends beyond the surface 23. The rib 24 has a fiat lower surface andsloping inner and outer surfaces 26, 27, each of. which may be formed asa cone having an apex half-angle of 16. The outer surface 27 leads tothe maximum external diameter of the punch 20, this maximum externaldiameter at the upper end of the surface 27 being slightly les's'thanthe internal diameter of the crown shell at the region where the topcorner radius 12 joins the skirt 13, wherewith the rib 24 can makecontact with the inner surface of the crown shell at this top cornerradius.

The platen 15 and the punch 20 are preferably heated to facilitate thethermoplastic flow of the material 17.

The punch 20 is brought down forcibly and the material begins to flowradially outwardly from the axis of the crown shell and towards the topcorner radius 12 and skirt 11 of the crown shell. This flow of thematerial 17 permits the punch 20 to move further into the crown shell sothat the outer edge of the projecting rib 24 on the punch 20 seats (Fig.3) in the top corner radius 12 near the juncture with the crown skirt11, thus forming a seal between the periphery of punch 20 and the crownshell. As the material 17 continues to flow, the periphery of the punch20 applies pressure to the periphery of the crown shell, therebypreventing flashing past the positive seal between the periphery of thepunch and the crown shell,

and also causing the peripheral parts of the domed crown shell surface10 to move downward toward the platen so that with the continueddownward movement of the central end surface 21 of the punch, acontinued outward flow of the material occurs to fill the space adiacentthe surfaces 22, 23 and the rib 24, therewith forming the cushion padwith a thin central portion 25 opposite the flat end surface 21 of thepunch and a thicker annular portion 26 formed by the walls at theshoulder 22, the surface 23, and the inner surface of the peripheral rib24. It will be noted that the presence of the rib 24, and the contact orclose cooperation of the outer surface of the punch 20 and the topcorner radius 12 of the crown shell, at a circular line near thejuncture of the corner radius with the skirt 11, totally prevents theextrusion of flash, or at most permits only such minor quantity ofmaterial to move across the lower surface 25 of the rib 24 that finallyno such material lies adjacent or in the corrugated parts of the skirt.In the relative positioning of parts shown in Fig. 4, the punch 20 hasacted upon the mass 17 of material to give it a final shaping, andtherewith the bottom 10 of the crown shell has been flattened and restsupon the platen 15 over essentially its entire area.

The pressure contact as shown in Fig. 4 may be maintained for the periodof time desired and requisite for the shaping operation; and if thematerial of the mass 17 is of curable or vulcanizable nature, the punchand platen may then be maintained at a temperature for curing orvulcanizing the material, the contact being maintained until the mass isform-maintaining, or even until the curing or vulcanizing has beencompletely efiected.

When the pressure between the punch 20 and the platen 15 is released,the material of the crown shell returns elastically, and the crown sealthus produced is as shown in Fig. 5, being essentially in the samerelative position of parts as in Fig. 1. In practice,'it has been foundthat molding pressures up to 150 pounds can be employed with thepresently standard sheet metal crown shells, without permanentdistortion thereof.

In the preferred illustrative formof Fig. 5, it. will be noted that thecushion pad has the thin central portion;

inter-solution.

30 which may have a thickness of 4 to 10 thousandths of an inch:together with a thicker annular portion 31 for engaging the lip of thecontainer to be closed by the crown seal, having a thickness of 20 to 38thousandths of an inch at its thickest part. In a crown seal for abottle, for example, using a shell of standard diameter, the centralportion 30 (formed by part 21 of the punch) may be about 0.735 inch, theannular portion 31 may be formed by a conical punch surface having anangle of 12 relative to the flat bottom 21 of the punch: and the sidefaces of the rib 24 may each have an angle of 16 relative to the axis ofthe punch, the flat on the rib having a width of about 0.008 inch, withan external diameter of about 1.026 inch and forming a plane spacedabout 0.030 inch from the plane of the bottom 21; and the punch bodyhaving a diameter of 1.0525 inch. Thus, in this preferred form, theannular portion is not of uniform thickness, but has a greater thicknessat its outer periphery 27 than at the inner periphery 28. An incidentalresult of employing the rib 24 on the punch, is that the annular portion31 has a beveled outer edge 32 leading from the point of maximumthickness, in the illustrative form, to the top corner radius of themetal shell, thus providing a shape which permits some displacement ofthe annular portion 31 under the pressure and conditions of sealing andcrimping, and assists in assuring adequate and proper contact with thecontainer lip which permits the completed seal to resist leakage of gasor product through the seal.

The material employed for the plastic mass 17 may be of any suitablethermoplastic elastomer type, competent to resist the contents of thecontainer to be sealed, such as natural or synthetic rubber compound,synthetic resin materials, and the like.

For example, paste resins can be employed, in which the basicingredients are an elastomer and a plasticizer therefor, the plasticizerbeing so selected that the clastomer is not actively soluble, i. e.essentially insoluble, therein at room temperature, but is soluble atsome elevated fluxing temperature. These two ingredients are groundtogether to form a paste which is fiowable at, say, to F, and the pastemay also include other components such as inert fillers to limitcutting, modifying resin to assist control of the physical properties,stabilizers for the resin and other components, waxes to preventblocking and to reduce moisture vapor and gas permeability, etc.However, these other materials are not essential in the composition, butmay be employed to contribute to the desired properties for theparticular employment. In general, the formulations described in theFoye United States Patent No. 2,489,407 and in South African Patent No.2556/47 may be employed, noting that the tiller and other componentsmaybe omitted if so desired. The elastomer component may be a vinyl resinof the class inclusive of polyvinyl chloride, copolymers of vinylchloride and vinyl acetate such as the 97:3 percent copolymer,vinylidene chloride polymers, and copolymers of vinyl chloride andvinylidene chloride. The chloride content should be high, when the sealis to resist aqueous liquids; such as 90 percent vinyl chloride in acopolymer.

Among the plasticizers useful are those which have a very slow wettingor dissolving action upon the selected vinyl resin at room temperatureand at temperatures up to around 115 F; The ester type plasticizers ofvinyl resins have this general characteristic, and require highertemperatures for producing penetration, diffusion, and

A'preferred plasticizer is dioctyl phthalate: others are dibutylphthalate, dioctyl sebacate, and tricresyl phosphate. The plasticizershould be liquid at the temperature of use. 7

The ratio of the elastomer and plasticizer, by weight, may be from 6:4to 4:6, with reference for a ratio of about 1:1.

Standard quantities of such paste resins may bedeposited in successivecrown shells, and these in turn brought onto a hot platen and engaged bythe hot punch. This engagement may occur while the deposited mass isessentially in its original condition, or the loaded shells maypreviously be moved through an oven, for example, so that a preliminaryor partial curing is accomplished before the shaping is effected. Thepressure required for shaping the mass depends upon the compositionemployed and the degree of curing which has been effected prior to theengagement, and upon the temperature of the mass during the shapingoperation. In practice it has been found that paste resins in originalcondition require less than 30 to 50 pounds per square inch pressure forthe shaping operation itself, wherewith a total pressure of 100 poundsis effective with the standard size of crown seal for producing theshaping of the mass and also the aforesaid resilient flattening of thedomed bottom. ,Correspondingly, with partially or completely cured pasteresin masses, shaping has been accomplished in standard crown shellswith pressures of 150 pounds or less.

When a rubbery or other non-fluid composition is employed for the pad,the charge may be introduced into the crown shell in the form of a diskor partly shaped blank, the completion of the shaping and the adhesionbeing accomplished by the use of the hot platen and the hot punch 20. Asuitable rubbery composition has rubber as an elastomer base which canbe modified as desired by fillers, lubricant, and vulcanization agents.An illustrative formulation is:

Parts by weight Crepe rubber (natural latex rubber) 88 Semi-solidisobutylene polymer 12 Hydrated precipitated calcium silicate 63 Clay 65Zinc oxide 5 Stearic acid 2 Heptylated diphenylamine l Dipentamethylenethiuram tetrasulfide 1 Tetramethyl thiuram monosulfide 1 /2 It ispreferred to have the inner surface of the crown shells lacquered duringmanufacture. For example, a vinyl lacquer prepared as described in theMaier et a1. Patent No. 2,380,456, with 80 percent of vinylchloridevinyl acetate copolymer resin and percent of oleoresinousmodifier produces a satisfactory adhesion. When the crown seals are tobe employed with carbonated beverages, beer, fruit juices, vinegar,etc., it is preferred to employ a trimer lacquer having a correspondingsolids formulation of 80 percent of vinyl chloride-vinyl acetatecopolymerized in the presence of maleic anhydride as a modifier, forexample in the respective ratios of 85: 13:2, together with 20 percentof a phenolic resin derived from orthocresol. Either of these lacquerscan be prepared in an organic solvent, such as 70% xylol and 30%isophorone, with 20% solids, for roller coating. For spraying, morevolatile solvents, such as toluol, methyl ethyl ketone, and methylisobutyl ketone, can be used. After applying and drying, the coating isbaked.

Such an internal lacquer coating is illustrated by the inner lining 40in Fig. 5. The customary external advertising is also illustrated as anouter lacquer coating 41.

It will be understood that the invention is not restricted to the formsof practice shown, and that the same may be practiced in many wayswithin the scope of the appended claims.

I claim:

1. The method of forming a closure seal with a cushion pad in a closureshell, said shell having a resiliently yielding internally concave domedbottom portion joined by a top corner radius portion with a skirtextending from the top corner radius portion, which comprises depositinga charge of plastic material in the closure shell, engaging a limitedcentral part of the outer surface of the bottom portion with asupporting surface, engaging a punch end surface with said charge andpressing therewith against the same and producing plastic flow andadhesion over said bottom portion and toward the top corner radiusportion, effecting a sealing engagement of the periphery of said punchsurface with the top corner radius portion prior to the flow of thecharge material past said periphery and thereby confining the chargebetween said punch surface and the closure shell, continuing themovement of the punch surface toward the supporting surface while theperiphery of the punch surface remains in engagement with the top cornerradius portion so that the resilient domed bottom portion of the closureshell yields and is flattened and the charge material continues itsconfined flow for filling the spaces adjacent the container-engagingsurfaces of the cushion pad without formation of flash material, andthereafter withdrawing the punch surface and permitting the saidflattened bottom portion to return to domed shape.

2. The method as in claim 1, in which the punch has at its periphery anaxially extending rib for said sealing engagement with the top radiusportion of the closure shell, and said punch end surface also hasradiallyinward from said rib a rebated annular surface portion effectivefor providing in the cushion pad a thick part for engaging the containerlip, said rib being effective in determination of the flow of theplastic material adjacent said top corner radius portion.

3. The method as in claim 1, which includes interposing a rib projectingaxially from the aforesaid punch end surface into the path of radiallyoutward flow of the plastic material for determination of such flowadjacent the said top corner radius portion of the closure shell, saidinterposing being accomplished concurrently with effecting the saidsealing engagement.

4. The method as in claim 1, in which the plastic material for thecushion pad is a thermoplastic, and which includes the heating of thepunch and supporting surfaces for assuring the flow of the confinedplastic material into conformity with the closure seal and the punchsurface.

5. The method as in claim 1, in which the material for the cushion padis a paste resin comprising of a thermoplastic resin and a plasticizerwith the thermoplastic resin not actively soluble in the plasticizer atroom temperature and soluble therein at an elevated fluxing temperatureto form an elastic mass, and in which there is heating of the punch andsupporting surfaces to a temperature for effecting solution of thethermoplastic resin in the plasticizer.

6. The method as in claim 1, in which the material for the cushion padis a vulcanizable elastomer composition capable of thermoplastic flow,and in which there is heating of the said punch and supporting surfacesto a temperature effective for softening the said composition uponcontact therewith and initiating vulcanizing thereof.

References Cited in the file of this patent UNITED STATES PATENTS Re.19,536 Parks Apr. 16, 1935 304,252 Beher Aug. 26, 1884 345,962 FinchJuly 20, 1886 713,844 Boylan Nov. 18, 1902 827,799 Grove et a1 Aug. 7,1906 1,087,710 Bogdanffy Feb. 17, 1914 1,209,980 Lawson Dec. 26, 19161,486,937 Taliaferro Mar. 18, 1924 1,928,987 Warth Oct. 3, 1933 FOREIGNPATENTS 587,355 Great Britain Apr. 23, 1947

